The best advice I can give is TRUST God completely to lead you to the person, and to give you perfect instruction and anointing to say exactly what needs to be said to that person.
It doesn't always require a long drawn out sermon to reach someone for Christ, complete honesty is a very special requirement that MUST never ever be forgotten.
God also does not require that you have the entire Bible memorized word for word either, even if you have NEVER read ONE verse, IF God sends you to witness to someone and there arises a need for you to quote a scripture God is well able to fill YOUR mouth with HIS word!
Believe me when I say sinners KNOW if you are truly sincere when you say you really care about their souls or if you are just another prissy Church member out to reach some monthly church witnessing quota!
I know for I was once one of the worst of the worst sinners and I had more than one Pastor or church group come to my home to witness to me, and more than once I scared more than one Pastor and church group away very violently and very often with extreme hostilities and even more extreme vulgar cursings!
BUT GOD!
Example:
Once a few years back my wife and I had attended a revival service at a church that was about 40 miles from were we live in Arkansas.
We had planned on stopping at the brand new Wal Mart that had just been completed in our home town (Greenwood Arkansas) and on the way there there were also 4 additional Wal Marts that we could have just as easily stopped at, BUT we heard the Holy Spirit very strongly instruct us to travel to a Wal Mart in Poteau Oklahoma which was about 60 miles from where we had attended the revival.
We obeyed the voice of God and went to Poteau praying all the way for God to reveal to us exactly why he had instructed us to go there.
On the way we heard God tell us that when we got there we would meet a tall young thin dark haired man and he would be the one that God had sent us to.
We got to the Wal Mart in Poteau Oklahoma and started walking around in the store looking for this tall thin young dark haired man that we knew God had sent us to minister to.
We did have more opportunites to minister to others in the store, but none resembled in anyway the young man we felt God had described to us, finally feeling a little frustrated and yet also satisfied that we had obeyed Gods direction we started toward the front of the store.
Just as we turned into the last aisle before we would be in the front of the store about fifty feet ahead of us a tall thin young dark haired man turned and stepped into the same aisle and began to walk toward us, we both knew immediately that this was certainly the young man God had been speaking to us about earlier that night!
He was 16 years old and he lived about fifty miles in the other direction from that Wal Mart and he said that there were also other Wal marts that were MUCH closer to his own home than this one was but for some reason he had feltt he needed to come to this particular Wal Mart and even though he could not understand why he had.
We spoke to the young man for a short time probably less than fifteen minutes sharing with him how God had instructed us to come there and how God had told us that we would meet a tall thin dark haired young man that God wanted us to minister to.
He was absolutely amazed, but more than this he was touched by the sincerity of our hearts towards him and especially our absolute total honesty with him about the love of Christ for him.
The young man gave his heart and life to Jesus right there in that Wal mart store!
Afterward he shared with us with tears in his eyes that his own mother and father and all of his Grandparents were all Christians and they had all been trying for a long time to get him to go to church with them but he had always refused, then he smiled and said he would wake his mom and dad up as soon as he got back home and tell them what had happened to him.
I don't know about any of you but I am absolutely certain there was probably just as much celebration in that young mans home that night and at his Grandparents homes when their son and daughter called them and told them what had happened that night to their Grandson as there had certainly been when he gave his life to Jesus there in the aisle of that Wal mart that night!
IF God says go, just GO he will take care of everything else!